Potassium channel openers: pharmacological and clinical aspects

Opening of plasmalemmal K+ channels leads to cellular hyperpolarization which, in excitable tissues possessing voltage-dependent Ca2+ channels, prevents the opening of such channels and thus prevents excitation. In the last few years, an increasing number of compounds have been identified which elicit their effects by opening K+ channels, preferentially in smooth muscle, but also in other excitable tissues. These include the novel benzpyrans, cromakalim and bimakalim, the thioformamide aprikalim, and also well known antihypertensives such as minoxidil sulphate, diazoxide and pinacidil. After a short overview of the various families of K+ channel openers (KCOs), their basic pharmacological properties, including inhibition by the sulfonyl ureas (such as glibenclamide) are presented. The actual discussion concerning the type of K+ channel(s) opened by these compounds and their mechanism(s) of vasorelaxation will be reported. The therapeutic potential of these compounds in the cardiovascular field (as antihypertensives and, in particular, as anti-ischemic agents in heart and skeletal muscle), and in asthma (where they reverse established airway hyperreactivity) will also be discussed. Improved tissue selectivity may be the essential pre-requisite for true clinical success of this class of compounds.